The quantitative evaluation of HTLV-I proviral DNA was determined to evaluate the Tax/Tex mRNA expression level for HTLV-I viral load. Some patients with HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) have higher viral load than HTLV-I carriers without HAM/STSP in their PBMNCs. Tax/Rex mRNA could not be detected by the PCR method. PCR plus Southern blotting with chemiluminescence method is being developed to detect the Tax/Rex mRNA.